I don't know how OS X handles its virtual memory. Windows XP uses C:/PAGEFILE.SYS for the virtual memory and C:/HIBERFIL.SYS for sleep mode. Linux and AmigaOS 4.1 need a SWAP partition for this. But in OS X I don't find similar things.

I did a bit research but what I found wasn't really informative. But I read that some programs are reserving a specified amount of RAM (virtual and real) although they aren't using it completely. For example, if you run Parallels in which the virtual machine is set to 1 GB RAM Parallels must allocate 1 GB minimum, even if the virtual machine doesn't need it.

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2 Opteron systems: OSx86 10.5.8, Andy's 9.8.0 kernel, Asus A8N-SLI Premium, Opteron 185 o'clocked @ 2 x 2,95 GHz (2nd system 2.6 GHz), ATI Radeon HD2600XT 256MB Dual-Monitor 2x HP L2035, 4 GB RAM, Griffin FireWave as main audio device, Marvell + nForce LAN, Asus U3S6 USB3/SATA6 card, 5,5 TB harddisk, Firewire 800 card, Apple Remote + eHome IR receiver, 2x Wacom serial graphics tablet, Canon Pixma iP4700, Logitech Internet Navigator wireless keyboard/mouse combination.

My Audio stuff: M-Audio Transit USB (default audio), M-Audio ProFire 610, M-Audio ProFire Lightbridge (34 channels) using Creamware A16 ADAT converter • MIDI: M-Audio Midiman 4x MIDI interface • Behringer Audio Mixers: Xenyx 1002, Xenyx 1002FX, Xenyx 1202FX, Eurorack UB1002FX, Eurorack MX1804FX, Eurorack MX262A • FX devices: Lexicon MPX100 DSP, Behringer DSP-1000 Virtualizer, Behringer MiniFEX 800 DSP, Behringer Multicom Pro MDX4400 compressor • RETRO: MSSIAH midi/sequencer/synthesizer cardridge for the C64 (Dual-SID), Steinberg M.S.I. MIDI Interface for C64